The tripartite motif (TRIM) family of proteins are characterized by a conserved TRIM domain that includes a coiled-coil region, a B-box type zinc finger, one RING finger and three zinc-binding domains. Staf-50 (50 kDa-stimulated trans-acting factor), also known as TRIM22 (tripartite motif-containing 22), RNF94 or GPSTAF50, is a 498 amino acid cytoplasmic protein that belongs to the TRIM family and, characteristic of TRIM family members, contains one RING-type zinc finger, one B box-type zinc finger and one SPRY domain. Induced by IFN-å and IFN-∫, Staf-50 is strongly expressed in ovary, spleen, thymus and peripheral blood leukocytes where it is thought to mediate the antiviral effects of IFN proteins. Additionally, Staf-50 is present in leukemic cells, suggesting a role in cancer formation and metastasis. Staf-50 exists as two alternatively spliced isoforms which are encoded by a gene that maps to human chromosome 11.